1. Field of Invention
The present invention relates to a lens plate, and more particularly to a composite lens plate.
2. Related Art
With the increasing concern about energy saving and reduction of CO2 emission, many electrical appliances gradually develop toward high efficiency and low energy consumption. Especially, various lighting devices have developed from tungsten lamps and fluorescent lamps used in the past to currently adopted light emitting diodes (LEDs). Due to its small volume, high luminance, long service life, low power consumption and other properties, the LED has become a new generation lighting device. For example, in Taiwan, all traffic lights use LED lighting devices. Since an LED lighting device includes many LEDs, the traffic lights can achieve a warning effect even if several LEDs fail.
In addition to the application in the traffic lights, the LED lighting devices are also commonly used in street lamps. When applied in street lamps, the LED lighting devices need to meet the requirements for high luminance, low power consumption, particular illumination range (also referred to as light distributions), and the like. For the particular illumination range, different local governments have different regulations on light distributions generated by the street lamps. Here, the so-called light distributions refers to an illumination range formed by light projected from a lighting device on a road surface.
Several methods are usually used to enable an LED lighting device to meet the requirement for a particular light distributions. In a first method, a lens plate is disposed in front of the LED lighting device, so as to refract light emitted by all LEDs to a predetermined position. In a second method, LEDs are properly arranged so as to achieve a required light distributions. In the above two methods, when meeting the requirements for different light distributions, at least one mold needs to be designed for each light distributions, so as to fabricate a lens required by the light distributions. Therefore, when bidding for the manufacturing of street lamps for different road sections, a manufacturer needs to design different molds, which increases the cost and is not economical.